1. Technical Field
Embodiments of the subject matter disclosed herein generally relate to methods and systems and, more particularly, to mechanisms and techniques for protecting a device from erosion and/or material buildup.
2. Discussion of the Background
During the past years, the presence of compressors is more visible in the oil and gas industry. The compressors are used not only to extract oil and gas, but also to transport the oil and gas from the extraction point to the location of the consumer. The compressors are also used in a wide variety of petrochemical processes, as for example, generating Liquefied Natural Gas (LNG), ethylene, polyethylene, etc.
Thus, the construction and maintenance of compressors is becoming more important for these industries. While many types of compressors exist, for example, centrifugal compressors, screw compressors, axial compressors, etc., most of the compressors are facing similar problems. These problems include but are not limited to, material buildup on various components of the compressors and/or erosion of some components of the compressors.
One mechanism that causes the degradation of the compressors is fouling. Fouling is caused by the adherence of particles to airfoils and annulus surfaces of the compressor. The adherence may be caused by oil mist, water mist or other mists that may be present in the compressor. The result is a build-up of material that causes increased surface roughness and to some degree changes the shape of the airfoil. FIG. 1 shows such a material build-up on an impeller of a centrifugal compressor. FIG. 2 shows a material build-up on a discharge cone of the compressor. While the airfoil is discussed in particular, the same is true for other components of the compressor. As the contaminants are small, for example, some of them may be smaller than 2 μm, fouling is currently eliminated by cleaning.
This means that the compressor is constantly inspected and when the build-up is detected, the compressor is taken out of service. Then, the components of the compressor that experience build-up are cleaned, by either being removed from the compressor, or, if the access to the affected compressor part is open, by cleaning the component while the same remains attached to the compressor. All these operations require that the process performed by the compressor be stopped, i.e., the whole production cycle is affected by this cleaning process. This results in down production time and loss of production, which are undesired by the operator of the compressor.
Hot corrosion is another mechanism that degrades parts of the compressors. Hot corrosion is the loss of material from flow path components caused by chemical reactions between the component and certain contaminants, such as salts, mineral acids or reactive gases. The products of these chemical reactions may adhere to the components of the compressor as scale. High temperature oxidation, on the other hand, is the chemical reaction between the components metal atoms and oxygen from the surrounding hot gaseous environment. The protection through an oxide scale will in turn be reduced by any mechanical damage such as cracking or spalling, for example during thermal cycles.
Another mechanism that may damage the components of the compressor is erosion by impact. Various particles are impinging on flow surfaces of the compressor while those particles are circulated through the compressors. These particles typically have to be larger than 20 μm in diameter to cause erosion by impact. Erosion is probably more of a problem for aero engine applications, because state of the art filtration systems used for industrial applications will typically eliminate the bulk of the larger particles. Erosion can also become a problem for driven compressors or pumps where the process gas or fluid carries solid materials. Damage is often caused by large foreign objects striking the flow path components. These objects may enter the compressor with the gas stream. Pieces of carbon build-up breaking off from fuel nozzles can also cause damage to the components of the compressors.
All these processes, i.e., erosion, deposits, or damages to the airfoil change the geometric shape of the airfoil. The deterioration of the blades of these devices is accompanied by changes in exit angles and increased losses. If the blade operates at or near transonic velocities, deposits or added roughness (with the associated growth in boundary layer thickness) will also reduce the possible flow through the blade row. Thicker boundary layers on the blades and sidewalls reduce the flow capacity, especially near choking conditions. On the other hand, if the trailing edge erodes, the throat width of the blade is increased, thus allowing more flow, but with less head reduction. Except for cleaning the affected components of the compressors, there are no known efficient methods for preventing the above-noted processes.
Accordingly, it would be desirable to provide systems and methods that avoid the afore-described problems and drawbacks.